1. Field of the Invention
The present invention relates to a solid electrolytic capacitor such as tantalum capacitor or aluminum capacitor. More specifically, the present invention relates to a surface mounting type solid electrolytic capacitor which incorporates a safety fuse wire which breaks upon an excessive temperature rise and/or upon passage of an overcurrent.
2. Description of the Related Art
A prior art surface mounting type solid electrolytic capacitor incorporating a safety fuse wire is disclosed in Japanese Patent Application Laid-open Nos. 63-84010 and 2-1055103 for example. Specifically, the prior art capacitor comprises a capacitor element and a resin package enclosing the capacitor element. The capacitor element has a chip electrically connected to a cathode lead through a safety fuse wire, and an anode wire connected directly to an anode lead. The anode and cathode leads project out of the package from opposite side surfaces thereof and are bent toward the underside of the package.
In use, the prior art capacitor can be conveniently mounted to a surface of a printed circuit board by soldering the projecting portions of the respective leads, and the resulting fixation can be rendered very firm. However, the presence of the two leads makes the size and weight of the capacitor correspondingly large, which is contrary to the general need for a size reduction while realizing a capacitance increase for a given size. Further, the existence of the leads also adds to the manufacturing cost.
In view of these problems, Japanese Patent Application Laid-open No. 7-29780 discloses a leadless solid electrolytic capacitor. Specifically, the leadless capacitor disclosed in this Japanese document comprises a capacitor element which has a capacitor chip and an anode wire projecting from the chip. The capacitor element is enclosed in a resin package with the tip of the anode wire exposed at a first side surface of the package. A safety fuse wire is connected to the chip of the capacitor element and has a tip exposed at a second side surface of the package opposite to the first side surface. The first side surface of the package is covered by an anode-side terminal electrode in electrical conduction with the exposed tip of the anode wire, whereas the second side surface is covered by a cathode-side terminal electrode in electrical conduction with the exposed tip of the fuse wire.
Apparently, the leadless capacitor described above is advantageous in that the absence of leads contributes to a reduction of size, weight and manufacturing cost while realizing a capacitance increase. However, since only the first and second side surfaces of the package on which the respective terminal electrodes are formed can be utilized for soldering at the time of mounting the capacitor to a circuit board, there is a weakness with respect to the bonding strength of the soldering.
On the other hand, it is necessary either to decrease the thickness (diameter) of the fuse wire or to increase the length of the fuse wire for improving the melt-cut characteristics thereof. Of these two requirements, a thickness decrease will result in difficulty of bonding the fuse wire to the capacitor chip. Thus, the only possible solution is to increase the length of the fuse wire. However, according to the structure of the prior art leadless capacitor, since the fuse wire is made to extend straight from the chip to the second side surface of the package, the package or the capacitor as a whole need be elongated to increase the length of the fuse wire for improving the melt-cut characteristics thereof, consequently resulting in an increase of size and weight of the capacitor.